1. Technical Field
The present invention relates generally to exhaust filtering and, in particular, to a filter system, regeneration system for the filter system, a combined soot removing system and applications of those systems. In addition, this invention relates to a particulate filter unit usable with one or more second stage particulate and nitrogen oxide filter units.
2. Related Art
Filtering of exhaust is a well-known mechanism to reduce pollution. Related art devices have suffered from a number of drawbacks. For instance, most of the filters are adaptations of substrates used for automotive catalytic converters in which alternating channels are plugged to force the gas through the substrate walls. A number of other filter configurations and materials have been tried, but none have been robust enough or cost effective enough for widespread use. Also, once the particulates or other materials have been collected, they must be removed before the filter can function effectively. This is typically accomplished by igniting and burning the collected burnable particulates using a variety of techniques. Current techniques in the art of regeneration are expensive, complex, and many are outright hazardous, e.g., some use explosive, compressed gas or highly flammable (compared to diesel fuel) liquids.
In addition, the catalytic converter materials were designed to operate at much lower temperatures than can be reached during an uncontrolled regeneration (rapid, uncontrolled burning of the soot collected in the filter). In many cases, the filter media cracks, melts, or is otherwise damaged by either vehicle induced vibration or very high temperatures. In addition, many filters include two or more integral filter sections for filtering different pollutants. Unfortunately, these filters make regeneration difficult. Further, when one filter section is in need of repair, all of the sections must be replaced.
Another problem with related art devices is their inability to accommodate different applications because of their inflexible size. A new mold must be made for each different size filter unit, which dramatically increases cost or limits the ability to tailor the filter for the application. U.S. Pat. No. 5,250,094 to Chung et al. discloses a filter construction having a number filter sections 114. Unfortunately, the device is limited in application by the size of the enclosure.
Related art devices also do not adequately provide a regeneration system that is safe and controllable. In particular, U.S. Pat. No. 5,820,833 to Kawamura includes an electric wire net that is integral with a filter, i.e. in-filter regeneration. Since the regeneration system and filter are inseparable, the device may be subject to vibrations that may induce damage. U.S. Pat. No. 5,394,692 to Teuber-Ernst discloses a separate regeneration system that is fired by an explosive gas, which is an unsafe situation when in an environment where other fuel sources are nearby. Another problem with these regeneration systems is their inability to adequately control the rate of burn and, therefore, the temperature of the filter during regeneration. Many filters cannot withstand the repeated exposure to higher temperatures caused by some regeneration systems. Further, the potential for regeneration to proceed uncontrollably is potentially dangerous due to the extreme amount of heat that is generated by the burning soot.
Accordingly, there is a need in the art for a filter that includes separate filtering sections for ease of repair and regeneration. Furthermore, there is a need for a readily size-adjustable filter system. It would also be advantageous if this filter could be retrofitted to a variety of exhaust producing devices that exhaust a variety of different pollutants. Moreover, there is also a need for a safe and controllable regeneration system. A system that combines the above filter and regeneration system would also be advantageous.
In addition, a system with improved particulate removal would be advantageous.